The present invention relates generally to housings for fiber optic components and, more specifically to housings for fiber optic couplers.
Optical fibers are thin transparent fibers of glass or plastic enclosed by material(or cladding) having a lower index of refraction and transmit light throughout their length by internal reflections. The fibers and cladding are typically enclosed in a protective polymer jacket.
Fiber optic couplers connect one or more optical fibers together allowing electromagnetic waves to propagate through the connected optical fibers. Such couplers are used in fiber optical communications systems, optical sensors, fiber optic gyros, and many other devices.
One type of fiber optic coupler is fabricated by fusing and tapering two or more optical fibers together. The fibers or both the fibers and cladding are brought together, and heated to fuse and taper the fibers (and cladding) resulting in a fused and tapered region for coupling of optical power.
Fiber optic couplers are extremely fragile and must be protected from most environmental conditions. FIG. 1 shows a cutaway view of prior art housings for optical couplers.
The housing 10 encloses the fiber optic coupler 11. Coupler 11 couples optical power between optical fibers 12. Optical fibers 12 have a jacketed portion 12A and a jacketless portion 12B. The protective jacket is removed from the area of the fiber optic coupler 11 prior to biasing the optical fibers together. Coupler 11 is enclosed in protective body 13 which is formed from a glass tube. Slot 13A is cut in protective body 13 providing access into the interior receiving space 13B. The protective body 13 is encased in a cylindrical stainless steel tube 14 for added protection. Adhesive 15 is applied near each end of protective body 13 securing jacketed portions 12A to the interior of protective body 13 and suspending complete 11 away from the interior walls of protective body 13. Finally, a silicon material (not shown) fills the receiving space 13B surrounding coupler 11. The silicon material cures into a resilient solid which supports coupler 11 and dampens vibrations and shock imparted to housing 10.
FIG. 2 is a cross sectional view of the prior art along view 2--2 of FIG. 1. Jacketless optical fibers 12B are suspended in receiving space 13B and surrounded by silicon support material 20. Glass protective body 13 is encased by stainless steel tube 14. The thin wall glass tubing used in the prior art is susceptible to fracturing as indicated by arrows 21, due to repeated temperature cycles. It is believed that fracturing of the protective body directly leads to damage or failure of the enclosed optical component.
Several factors make fabricating a robust protective housing for optical components difficult. Three factors which must be considered when designing a housing include stress, vibration and shock, and refraction.
First, stress on the optical fibers and fiber optic components must be reduced or eliminated. Acute stress causes the fibers to break while lesser stress causes the optical properties of the fiber to change and degrade resulting in inefficient propagation of optical power. Stress is caused by pulling, bending, or otherwise applying force on an optical fiber.
One cause of stress is the result of thermal expansion and contraction of the fibers and the housing. When the housing and the fibers expand and contract at different rates, stress is induced in the optical fibers. The prior art reduced this problem by making protective body 13 out of glass which has the same thermal coefficient of expansion as the fibers so that both the protective body and the fibers expand and contract at the same rate. This reduces the expansion problem, however, adhesives 15 which secure the optical fibers in the protective body do not have the same coefficient of expansion as the optical fibers and impart stress to jacketless optical fibers. Also, these adhesives do not adhere well to either the jacketed or non-jacketed portions of the optical fibers. The prior art is careful to avoid this stress on the jacketless optical fibers by applying adhesive only to jacketed portions 12A of the optical fibers. As a consequence, the bare or jacketless optical fibers are subject to movement or sliding inside the protective jacket material which causes stress on the optical fibers and components.
Second, the fiber optic component must be protected from vibration and shock. The prior art uses a glass protective body to shield the component From vibration and shock. Adhesives are used to suspend the component in the protective body and away from the walls of the protective body providing further isolation from vibration and shock. As discussed above, however, adhesives impart stress to jacketless optical fiber because of the differing expansion characteristics of the adhesive and the optical fibers. Finally, the prior art surrounds the fiber optic component with a resilient silicon material to support and isolate the component from vibration and shock. Overtime, however, this resilient material hardens, shrinks, and separates from the walls of the protective body thus eliminating its effectiveness and inducing acute stress on the component.
Third, any type of housing or protection must not interfere with the optical transmission characteristics of the component or the optical fiber. Typically this requires that materials in contact with the optical fibers have a lower index of refraction than the optical fibers. This requirement severely limits the design of and materials used to construct housings for fiber optic components.
Clearly there is a need for an improved housing for fiber optic components and the like which provides improved stress, vibration, and shock protection over a wide temperature range.